This invention relates to a stopper to be used for plugging holes such as are bored in the floor panel of an automobile for the discharge of water.
As means for plugging the holes of this kind, there have heretofore been proposed various forms of stoppers made of rubber or flexible synthetic resins. The construction which is commonly involved in the stoppers of this kind widely known in the art comprises a flange portion adapted to come into face-to-face contact with the surface of a panel containing an opening and an insertion portion extended downwardly from the lower surface of the flange and adapted to be inserted into the opening in the panel. Generally, this insertion portion is formed so that the outer boundary thereof approximately conforms to the diameter of the opening in the panel, and it is provided on the outer circumferential wall thereof with an engaging portion adapted to come into fast engagement with the edge of the opening.
When such an ordinary stopper is to be set in position on the opening, the fastening is accomplished by forcibly pushing the insertion portion of the stopper down the opening thereby causing the engaging portion formed on the outer circumferential wall of the insertion portion in a diameter greater than the diameter of the opening to contract momentarily in the radial direction by virtue of the resiliency of the material of the stopper and, after the wall has slid past the opening, allowing the engaging portion on the wall to expand to its original shape and fasten itself to the opening. In consequence of the fastening, the opening is watertightly plugged by the stopper, with the outer circumferential wall held in tight contact with the inner wall of the opening and the aforementioned flange portion kept in face-to-face contact with the surface of the panel.
From the standpoint of the function to be fulfilled, the stoppers of this kind are required to possess watertightness and ability to provide tight fastening. In this sense, the aforementioned conventional stoppers are defficient in terms of tight fastening, although they are fully satisfactory in terms of watertightness. As described above, the conventional stopper is fastened to the opening by forcibly pushing the insertion portion of the stopper down the opening and thereby causing the engaging portion formed on the outer circumferential wall to contract temporarily in the radial direction by virtue of the resiliency of the material. The engaging portion proposed to date is formed throughout the entire outer circumferential wall of the insertion portion to meet the requirement that the engaging portion should be formed in a shape conforming to the shape of the opening. When the insertion portion is pushed down the opening, therefore, the engaging portion collides against the entire circumference of the opening. The resistance consequently generated is strong so that the insertion of the engaging portion past the circumference of the opening calls for a fairly large amount of force in spite of the resiliency of the material. This fact is appreciated more readily in the light of the fact that the opening in the panel is generally formed in the shape of a true circle and, by the same token, the insertion portion is given an outer boundary conforming to the shape of the opening. To be more specific, when in this case, the force is applied to insert the insertion portion past the opening after the entire engaging portion on the outer circumferential wall has collided with the entire circumference of the opening, the entire engaging portion tends to contract radially all at once. If, at this point, the force of insertion fails to act uniformly upon the entire engaging portion, only a part of the engaging portion is made to slide past the opening and the remaining part thereof is consequently suffered to expand to an extent of rendering the insertion rather difficult than otherwise.
Various measures have been tried to cope with this problem. Among the measures proposed to date is counted the concept of giving a small thickness to the outer circumferential wall of the insertion portion thereby enhancing the flexibility of the insertion portion itself and facilitating the radial contraction of the engaging portion. The invention disclosed in Laid-open Utility Model Publication No. 2821/1978 may be cited as one version of this concept.
In spite of the effort, the fact still remains that the entire engaging portion collides with the entire circumference of the opening during the insertion. This concept, therefore, has a disadvantage that since there exists a constant force tending to keep the circumference of the wall in its original length, the force of insertion, if not exerted uniformly throughout the entire engaging portion, predominantly causes outer deformation of the wall and consequently allows a part of the engaging portion to slide past the opening and repels the remaining part, with the result that the difficulty involved in the passage of the entire engaging portion through the opening will become only conspicuous.